Plastic container made from a fusion blend of post consumer plastic and ethylene polymers

ABSTRACT

A plastic container made from a fusion blend of a post consumer resin and a high density polyethylene copolymer resin. The post consumer resin is primarily a high density homopolymer and may contain small amounts of colored plastic containers and propylene resin. The physical properties of the container including stress crack resistance are maintained as contrasted to the loss of such physical properties that have been heretofore resulted from the use of post consumer resins.

This is a continuation of Ser. No. 08/219,810 filed on Mar. 29, 1994,which was a continuation of application Ser. No. 07/842,839, filed Feb.29, 1992, abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION

In the use of plastic materials for containers such as bottles, it hasbeen found desirable to attempt to recycle and reuse the plastic whichis commonly known as post consumer plastic (PCP) or post consumer resin(PCR). In attempts to make containers from such materials, it has beenfound that the properties have been adversely affected.

Specifically when containers are made from post consumer high densitypolyethylene homopolymers (HDPE) container scrap, it has been found thatthe containers have diminished physical properties and particularlydiminished resistance to stress cracking. Such containers made of highdensity polyethylene homopolymers also have been used for packaging ofcertain types of liquid detergent products. The use of such containersto package liquid detergent products has been somewhat restricted,however, by reason of the fact that many types of liquid detergentproducts accelerate the tendency of the container to exhibit stresscracking. Stress cracking is evidenced by the appearance of hazy cracksin the container which are aesthetically unpleasing to the ultimateconsumer. In extreme cases, stress cracking can lead to leakage of thecontents from the container. Stress cracking can occur when thecontainers are for liquid products including liquid detergents andliquid hypochlorite bleaches.

It has been suggested that such post consumer resin be utilized becauselarge quantities of high density polyethylene post consumer resin areavailable due to the extensive use of high density polyethylene in largecontainers for milk and water. Post consumer resin from such containerscontains contaminants of paper and other plastic resins, for example,from closures such that it has been generally thought that it can not beused to make satisfactory plastic containers.

Accordingly among objectives of the present invention are to provide ablend of post consumer resin from high density polyethylene containersand the like which will have substantial resistance to stress crackingand which will have minimal diminution in other physical propertiespermitting its use for various kinds of containers, that is forcontaining various products.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the invention, a plastic container made from a fusionblend of a post consumer resign and a high density polyethylenecopolymer resin. The post consumer resin is primarily a high densityhomopolymer and may contain small amounts of colored plastic containersand propylene resin. The physical properties of the container includingstress crack resistance are maintained as contrasted to the loss of suchphysical properties that have been heretofore resulted from the use ofpost consumer resins.

In accordance with the invention, pellets of a homopolymer high densitypolyethylene resin from post consumer resin (PCR) and pellets of avirgin high density polyethylene copolymer were mixed and fusionblended. Containers were blow molded and subjected to testing for stresscracking, top load and drop impact.

The blends of the present invention contain about 15-50% by weight ofpost consumer resin and about 50-85% by weight of virgin high densitypolyethylene copolymer resin.

Post consumer resin contains primarily the plastic from high densitypolyethylene homopolymer containers used for packaging milk and smallamounts of colored plastic containers and possible polypropylene resinfrom syrup bottles, multi-layer ketchup bottles and caps. Such postconsumer resin has the properties set forth in the following Table I.

                  TABLE I                                                         ______________________________________                                        PROPERTY            SPECIFIED VALUE                                           ______________________________________                                        Material Density    .961 ± .002 natural                                    Melt Flow - Melt Index                                                                            0.75 ± 0.2 dgm                                         Polypropylene       Not to exceed 3%                                          (Includes Multi-layer Bottles)                                                Fines               <0.01%                                                    Moisture            <0.05%                                                    Contamination                                                                 Paper               <0.01%                                                    Plastic-Dens. >1.0 gm/cc                                                                          <0.1%                                                     Metal fragments     None                                                      Other (glass, stone)                                                                              None                                                      ______________________________________                                    

The virgin high density copolymer resin contains linear high-densityethylene polymer. The linear high-density ethylene copolymer included inthe blends will have a density of at least about 0.94 gm/ml, a meltindex of less than about 0.5 gm/10 min. and will have polymerizedtherein at least about 98 mol % ethylene with any comonomer polymerizedtherein being an alpha-monoolefin containing about 3 to 12 carbon atoms.Such linear high-density ethylene polymers are known and reported in theart and are commercially available from numerous commercial producers.Such linear high-density ethylene polymers are prepared by polymerizingethylene, optionally in the presence of an alpha-monoolefin comonomercontaining 4 to 12 carbon atoms in the presence of certain metalliccatalysts such as chromium catalysts, e.g. CrO₃ supported onsilica-alumina supports, and the Ziegler-Natta catalysts, e.g. TiCl₃employed in conjunction with certain aluminum alkyl cocatalysts. Therequisite density and melt index desired in the polymer are obtained byproper control of polymerization conditions including temperature,pressure, comonomer concentration, and the concentration of telegenatingagents such as hydrogen. The preferred linear high-density ethylenepolymers will have a density of at least about 0.94 gm/ml. Theespecially preferred polymers will have a density of at least about 0.95gm/ml. Stress crack resistance is conventionally conducted with testmethods as established by Technical Bulletin PBI 11-1978 of the PlasticBottle Institute, Rev.1-1991 or ASTM D2561-70 (Reapproved 1989).

    ______________________________________                                        The following Table II summarizes one set of tests that have                  been conducted.                                                               32 OZ. PINCH WAIST OVAL                                                       RUN#        1      2      3    4    5    6    7                               ______________________________________                                        % PCR              25     40   50   60   75   100                             % Virgin Copolymer                                                                        100    75     60   50   40   26                                   Gram Weights                                                                              46.54  46.80  46.45                                                                              46.45                                                                              46.61                                                                              47.17                                                                              46.53                           (20 Bottles)                                                                              .338   .263   .2.44                                                                              .169 .270 .229 .228                            Mean                                                                          STD. Dev.                                                                     TOP Load    37.2#  41.8#  43.2#                                                                              43.7#                                                                              47.9#                                                                              44.4#                                                                              45.8#                           (10 Bottles)                                                                  Pounds                                                                        Drop Impact Test                                                                          7.36'  8.44'  8.96'                                                                              8.18'                                                                              7.40'                                                                              9.25'                                                                              8.13'                           (25 Bottles)                                                                  Bruceton Staircase                                                            EMFH                                                                          Stress Crack Test                                                                         42/**  4/27   3/8  8/12 1/2  1/1  1/1                             140 Degrees                                                                   (10 Bottles)                                                                  Days to                                                                       1st Fail/50% Fail                                                             120 Degrees 6/16   4/6    3/3  3/4  1/2  1/1  1/1                             (10 Bottles)                                                                  Days to                                                                       1st Fail/50% Fail                                                             ______________________________________                                         **Variable #1 Bottles had been in 140 Deg. Stress Crack for 51 Days as of     1/31/92, 50% Failure had yet to occur.                                   

Additional tests are summarized in the following Table:

                  TABLE III                                                       ______________________________________                                        Data Summary                                                                  16 oz. Oval                                                                   Control Virgin Copolymer                                                      15% Milk Bottle PCS Material                                                  30% Milk Bottle PCS                                                           45% Milk Bottle PCS Material                                                                 Averages                                                                      Control                                                                             15%     30%     45%                                      ______________________________________                                        gram weights (50 bottles)                                                     mean             34.83   34.77   34.95 35.22                                  std. dev.        .1870   .3058   .1992 .1918                                  top load test (10 bottles)                                                    pounds           66.6    73.2    68.6  60                                     drop impact test (25 bottles)                                                 Bruceton Staircase                                                                             9.5+    9.25    9.5+  9.5+                                   stress crack test (140° F.)                                            # of failures    0       0       0     0                                      ______________________________________                                    

The post consumer resin in pellet form was dry mixed with virgin 0.954density copolymer HDPE resin pellets and the blend was fed to themachine hopper. Melt temperature was approximately 400° F. No processingor machine changes were made in order to produce good quality bottles.

It can thus be seen that there has been provided a plastic container ismade from a fusion blend of a post consumer resin and ethylene polymerscomprising post consumer resin of homopolymer high density polyethyleneplastic and virgin high density polyethylene copolymer resin. Thephysical properties of the container including stress crack resistanceare maintained as contrasted to the loss of such physical propertiesthat have been heretofore resulted from the use of post consumer resins.

We claim:
 1. The method of making a plastic container comprisingproviding a fusion blend consisting essentially of a blend of:pellets ofpost consumer resin of homopolymer high density polyethylene resin; andpellets of virgin high density polyethylene copolymer resin, saidpellets of post consumer resin having a density of about 0.961±0.002gm/ml and a melt index of 0.75±0.2 dgm and polypropylene blended withthe post consumer resin not to exceed 3% by weight, said pellets ofvirgin high density polyethylene copolymer resin having a density of atleast about 0.94 gm/ml and a melt index less than about 0.5 gm/10 min.,said post consumer resin ranging between about 15% to 50% and saidvirgin high density copolymer resin ranging between about 50% to 85% byweight of the fusion blend, blow molding a plastic container from saidfusion blend to provide a plastic container such that the plasticcontainer has satisfactory stress crack resistance, top load and dropimpact properties.
 2. The method set forth in claim 1 wherein said postconsumer resin comprises at least of the fusion blend.